Fast, multi-responsive microgels based on photo-crosslinkable poly(2-(dimethylamino)ethyl methacrylate)

Multi-responsive microgels based on poly(2-(N,N-dimethylamino)ethyl methacrylate) were developed and their properties were investigated. The primary goal of this research was to speed up the stimulus-response time of the hydrogels to a level usable for actuator applications, by reducing the diffusion distance of water. The gels were prepared by a UV induced photodimerization of a copolymer of 2-(dimethylamino)ethyl methacrylate and 4-cinnamoyl-phenyl methacrylate. Patterning studies showed that these materials can be used as photo-resist materials with high resolution at short exposure times. They showed lower critical solution temperature behavior in water, as well as pH dependent solubility and swelling ratios. While 1 mm thick gels showed response times to temperature and pH-changes of several hours, Si-supported microgels of 300 nm thickness had response times in the range of only a few seconds. The copolymer was prepared by free radical copolymerization, and the reactivity ratios were determined with the extended Kelen Tudos method. Spin-coating of this copolymer on Si supports and subsequent UV-irradiation yielded microgels of variable thickness (200 nm–15 μm), which was determined by confocal scanning laser microscopy. Surface plasmon resonance spectroscopy measurements demonstrated the fast, stimuli-responsive swelling behavior, while differential scanning calorimetry gave insight into the morphology of the networks.